Guys,

This one is stumping me. I have a silverball mania with solenoid issues. The problem is on the MPU. I know because I have another silverball mania sitting next to it and swapped the MPUs and the problem follows the MPU. The problem seems to be somewhere either on or before the U11 PIA, or maybe after it? I have replaced the U11 socket and the U11 chip, I have tested continuity and all the resistors/caps in the solenoid data output section. All traces and components seem ok to me. But somehow momentary solenoid data lines C and D don't work right. They seem to be going low on the chip when I probe it with a logic probe, but when I probe the output connections on J4-1 and J4-2, the lines don't go low. But swapping U11 does nothing and there is good continuity everywhere.

I don't know. I'm sure I'm testing or observing something wrong because this doesn't make sense. But I'm hoping someone here can point me in a productive direction.

Thanks!
John

Thanks for the help....let me know what to check next.

John

Update - I finally figured this out. I started looking for other shorts or opens along the A,B,C, and D solenoid lines on the MPU. I found a 9.9Kohm resistance between C and D. I never really figured out how it had 9.9kohm, but I removed all solder from everything along those lines and resoldered everything very carefully. The 9.9k "short" went away and now the board works perfectly. Weird one. Thanks for trying to help me. I appreciate your time everyone.

John